PSY101 Chapter 5

One afternoon at my father's house, my stepmother Cyndi baked my favourite dessert: apple crisp. When she took it out of the oven, everyone exclaimed, 'That smell! It's delicious!'. I sniffed. Nothing.

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What you should be able to do after reading chapter 5

Describe the difference between sensation and perception; describe the processes involved in sensation, such as transduction and sensory coding; describe each of the sense organs and how they function; think of reasons why such senses have evolved

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Questions to think about

How many senses do we have? Are some senses more important to us than others? Which sense do we use least (or think we do) and why? Do the different senses function along similar lines, using similar mechanisms?

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Sensation and behaviour

Our senses are the means by which we experience the world; everything we learn is detected by sense organs and transmitted to our brains by sensory nerves.

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Sensory processing

Experience is traditionally divided into two classes: sensation and perception. Most psychologists define sensation as the detection of simple properties of stimuli, such as brightness, colour, warmth and sweetness.

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Transduction

Sense organs detect the presence of environmental stimuli provided by light, sound, odour, taste or mechanical contact. This information is transmitted to the brain through neural impulses - action potentials carried by the axons in sensory nerves.

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Sensory coding

Nerves are bundles of axons which can do no more than transmit action potentials (see Chapter 4). These actions potentials are fixed in size and duration; they cannot be altered.

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Anatomical coding

Since the early 1800's, we have known that the brain learns what is happening through the activity of specific sets of neurons. Sensory organs located in different places in the body send their information to the brain through different nerves.

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Temporal coding

Temporal coding is the coding of information in terms of time. The simplest form of temporal code is rate. By firing at a faster or slower rate according to the intensity of a stimulus, an axon can communicate quantitative information to the brain.

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Psychophysics

Psychophysics is the systematic study of the relation between the physical characteristics of stimuli and the sensations they produce (the 'physics of the mind').

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The principle of the just-noticeable difference

Ernst Weber (1795-1878), a German anatomist and physiologist, investigated the ability of humans to discriminate between various stimuli.

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Signal detection theory

Psychophysical methods rely heavily on the concept of a threshold, the line between not perceiving and perceiving. The just-noticeable difference can also be called a difference threshold, the minimum detectable difference between two stimuli.

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Vision

The visual system allows us to do many activities that we take for granted: in a quick glance we can recognise what there is to see - people, objects and landscapes - in depth and full colour.

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Light

The eye is sensitive to light. Light consists of radiant energy similar to radio waves. As the radiant energy is transmitted from its source, it oscillates.

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The eye and its functions

The eyes are important and delicate sense organs - and they are well protected. Each eye is housed in a bony socket and can be covered by the eyelid to keep out dust and dirt.

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Colour vision

Light consists of radiant energy having wavelengths between 380 and 760 nm. Light of different wavelengths gives rise to sensations of different colours. How can we tell the different between different wavelengths of light?

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The dimensions of colour

Most colours can be described in terms of three physical dimensions: wavelength, intensity and purity. Three perceptual dimensions - hue, brightness and saturation - corresponding to these physical dimensions describe what we can see.

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Colour mixing

Vision is a synthetic sensory modality. That is, it synthesises (puts together) rather than analyses (takes apart). When two wavelengths of light are present, we see an intermediate colour rather than the two components.

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Colour-coding in the retina

In 1802, Thomas Young, a British physicist and physician, noted that the human visual system can synthesise any colour from various amount of almost any set of three colours of different wavelengths.

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Negative after-images

Figure 5.16 demonstrates in interesting property of the visual system: the formation of a negative after-image. Stare at the cross in the centre of the imagine on the left for approximately 30 seconds.

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Defects in colour vision

Approximately one in 12 men has some form of defective colour vision. These defects are sometimes called colour-blindness, but this term should probably be reserved for the very few people who cannot see any colour at all.

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Psychology in action: What is it about the colour red?

A group of researchers from the University of Durham, UK, discovered an intriguing finding when they examined the success and failure of sportsmen and women who wore red or blue costumes (Hill and Barton, 2005).

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Cutting edge: Can colour generate heat?

Experiments have shown that people who sniff odourless water in bottles that are red associate this with warmth when they sniff with the left nostril: they associate green with 'cool' sensations when sniffing with the right nostril (Michael et al).

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Audition

Vision involves the perception of objects in three dimensions, at a variety of distances, and with a multitude of colours and textures. These complex stimuli may occur at a single point in time or over an extended period.

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Other cards in this set

Card 2

Front

Describe the difference between sensation and perception; describe the processes involved in sensation, such as transduction and sensory coding; describe each of the sense organs and how they function; think of reasons why such senses have evolved

Back

What you should be able to do after reading chapter 5

Card 3

Front

How many senses do we have? Are some senses more important to us than others? Which sense do we use least (or think we do) and why? Do the different senses function along similar lines, using similar mechanisms?

Back

Card 4

Front

Our senses are the means by which we experience the world; everything we learn is detected by sense organs and transmitted to our brains by sensory nerves.

Back

Card 5

Front

Experience is traditionally divided into two classes: sensation and perception. Most psychologists define sensation as the detection of simple properties of stimuli, such as brightness, colour, warmth and sweetness.